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Original Report |
1 Department of Radiology, North Western Adelaide Health Service, The Queen
Elizabeth Hospital Campus, Adelaide, South Australia 5011, Australia.
2 Present address: Department of Imaging, Mid Western Area Health Service, OBH,
Dalton St., Orange, New South Wales 2800, Australia.
3 Present address: Department of Neuroradiology, Vancouver General Hospital,
Vancouver, BC V5Z1P4, Canada.
Received February 13, 2003;
accepted after revision August 12, 2003.
Address correspondence to R. P. Davies.
Abstract
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CONCLUSION. MDCT is proposed as an alternative first-line investigation to locate lower gastrointestinal bleeding before placing the patient under observation or performing embolization or surgery.
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A test that would allow accurate identification of the site of bleeding and prediction of the treatment potential of arteriography and embolization would permit patients to be referred for targeted therapeutic arteriography or open surgery. We hypothesized that MDCT angiography could fulfill this role.
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MDCT images were obtained with a four-detector scanner (Aquillion, Toshiba, Tokyo, Japan) with a gantry rotation speed of 0.5 sec per rotation. The pitch and slice collimation were adjusted to optimize coverage of the abdomen in a single breath-hold. The images were acquired 30–40 sec after initiation of IV contrast injection of 75–100 mL of nonionic contrast material (Ultravist 370 [iopromide], Schering, Berlin, Germany] delivered at a rate of 3–4 mL/sec during the arterial phase imaging. Oral contrast material was not administered. A preliminary unenhanced series using a 5-mm slice thickness was performed in the latter part of the study to identify any preexisting hyperdense material in the bowel lumen. The range of scanning times was 12–29 sec, with the average being 19 sec. The reconstructed axial slice images were either 2- or 3-mm thick, and the reconstructed slice interval varied between 1 and 3 mm.
The images were interpreted by the attending radiologist (four different radiologists reviewed the study) using a commercially available software package (Plug N View 3D, version 3.1, Voxar, Edinburgh, Scotland) that allowed 2D, 3D, and multiplanar reconstruction (MPR) displays. The diagnosis and identification of the site of bleeding were based on the presence of extravasated contrast material in the bowel lumen seen on a combination of axial scans and MPR images.
The diagnosis of active bleeding was made when a linear, jetlike, pooled or swirled, ellipsoid focal collection of arterial density contrast material with a mean attenuation of at least 175 H was identified within the bowel lumen (Figs. 1A, 1B, 2, 3). Mucosal enhancement was differentiated as hyper-density confined to the bowel wall and confirmed on MPR images (Fig. 1A, 1B).
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To assess for possible mimics of intraluminal bleeding, we reviewed 315 consecutive abdominal MDCT examinations to act as a control group for other possible causes of hyperdense material in the bowel. These examinations were performed during the same period without oral contrast material for clinical indications other than gastrointestinal bleeding. One hundred forty-one of the 315 examinations were performed with IV contrast material. In cases in which densities were visualized, we reviewed the MPR images and calculated the mean attenuation values in the regions of interest.
Angiography and embolization were performed with a Multistar Plus angiography machine (Siemens, Forcheim, Germany). Selective catheterization using cobra-shaped, angled tip, and reverse curve catheters and superselective catheterization of mesenteric vessels using a coaxial technique with a 3-French microsystem (SP, Terumo, Tokyo, Japan) were performed. Hilal 0.018-inch microcoils (Cook, Queensland, Australia) were used to embolize the bleeding vessels.
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One patient underwent angiography on three separate occasions in addition to one scintigraphic and two MDCT examinations. On hospital day 1, the patient's MDCT scan showed a bleeding point, which led to the performance of conventional angiography followed by a technically successful embolization for angiodysplasia of the ascending colon. After the procedure, the patient was returned to the ICU, where anticoagulant therapy was begun for chronic pulmonary thromboembolism. The patient continued to experience melena, and MDCT repeated on day 3 showed no bleeding point, although the quality of this second study was suboptimal because of the presence of residual high-density extravasated contrast material in the patient's bowels. Conventional angiography also failed to reveal an active bleeding point. On day 12, a third conventional angiogram was obtained for continuing melena and again showed negative findings. The findings on a scintiscan obtained after the arteriogram were also negative. The melena eventually stopped on day 15 without intervention.
Interpretation of the MDCT scans took approximately 10–15 min using the multiplanar software. Causes of hyperdensities other than bleeding identified in the 315 control group members included colonic suture margins (Fig. 4), contrast material in the diverticula, and suspected foreign bodies.
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The potential advantages of using MDCT in the treatment of acute lower gastrointestinal bleeding include availability, speed, reproducibility, and noninvasiveness. Multidetector technology now allows coverage of the whole abdomen in the arterial phase after IV injection of contrast material. MDCT appears to be useful for accurately identifying the source of bleeding. MDCT successfully showed active bleeding in both the small bowel and the large bowel (Figs. 1A, 1B and 2). The small bowel is a rare source of bleeding in hematochezia, and current investigative options for diagnosis of its occurrence are problematic [11].
Although bleeding points are readily identified on axial scans, multiplanar reconstructions permit quick, confident, and accurate identification of bleeding sites as well as vessels for potential embolization. With the location of all bleeding sites identified in advance on MDCT, survey angiography is obviated, and the angiographer can immediately begin selective catherization of the targeted areas. Once a selective position close to a bleeding site has been reached, immediate embolization can be performed through the same catheter that was used to deliver contrast material for MDCT, with resultant savings in time, reduced angiographic contrast volume, and minimal fluoroscopic radiation dose compared with that delivered when survey angiography is the initial investigation.
Although the rate of bleeding detectable on MDCT has not been quantified, in this retrospective review, all bleeding points subsequently detected on angiography were visualized on MDCT. No patient with negative findings for bleeding on MDCT subsequently required surgery or intervention for continued bleeding. Positive MDCT findings for bleeding were highly predictive of a specific bleeding point. In patients with negative MDCT findings, conservative treatment was successful in all cases. Our results may be a reflection of selection bias or of the small number of cases in our study. False-positive and false-negative findings would be anticipated in a larger study because of the intermittent nature of hematochezia. Colonic bleeding may resolve spontaneously in up to 85% of cases [5]. Even massive hemorrhage may cease, and it can be impossible to determine the site or cause of the bleeding. It is also difficult to assess mild to moderate fluctuating hematochezia clinically because of the variability of intestinal transit time [1].
Patients discharged after a negative test result or successful intervention who did not present again at our institution within 30 days were considered to have ceased bleeding. Despite the small number of patients in our study, it appears that MDCT is a good method by which to predict positive angiographic results and to accurately locate the site of bleeding before surgery or embolization.
A randomized study to test detection of gastrointestinal bleeding on MDCT compared with detection on scintigraphy or survey angiography may not be ethically supportable because of the absence of a relevant control group; the life-threatening nature of the problem precludes use of the much slower scintigraphy, which often requires imaging over many hours. The limited availability of after-hours angiography and the relative accessibility of MDCT would also make a randomized trial comparing these two techniques for initial diagnosis difficult to perform. A targeted therapeutic arteriogram reduces time, radiation, and volume of contrast material.
There are limitations for MDCT in the assessment of hematochezia. MDCT may not be feasible to perform in patients who have renal failure, allergies to contrast agents, or residual contrast material in the bowel. Scintigraphy would be the preferred investigation in these situations. However, a clinical protocol in which MDCT scans were obtained in patients with hematochezia before placing them under observation or undertaking surgery or embolization could be prospectively assessed. Outcome measures could include the speed of identification of a bleeding point on MDCT angiography, any additional imaging studies requested, time elapsed before successful embolization was performed, costs of diagnostic workup and treatment, radiologist's or referring physician's confidence in the therapeutic decision making, and patient data related to the clinical problem such as the length of hospital stay. Hunink and Krestin [12] noted that new technology is often implemented as soon as available on the basis of subjective experience with a limited number of cases or a subjective expectation of the usefulness of the technology. Our judgment is that any introduction of this procedure should be accompanied by careful prospective assessment.
Use of MDCT in the assessment of hematochezia appears to meet the criterion of adequate technical performance. From our initial review, we believe that MDCT has a potential role in the evaluation of patients with hematochezia from the perspective of clinical impact on diagnosis, therapy, and prognosis. More rigorous assessment of the technique is warranted.
Acknowledgments
We thank Ross Harper, Scott Brown, and Steve Meinel of the radiology
department of the North Western Adelaide Health Service for their help in
patient data collection and on the technical aspects of MDCT, and Paula
Anderson for her help in image reproduction.
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